1. Field of the Invention
The present invention relates to a method for producing a polishing pad for use in a chemical mechanical polishing.
2. Description of the Related Art
Chemical mechanical polishing (CMP) is a procedure for planarizing the surface of a substrate with a polishing pad. CMP is generally applied in polishing lens, mirrors, substrates of liquid crystal displays, silicon wafers, and oxidation and/or metal layers on silicon wafers.
U.S. Pat. No. 6,454,634 discloses a polishing pad produced by a method comprising the steps of pouring thermoplastic foam resin in a circular mold to form a casting, skiving the casting into sheets, and mechanically machining macro-channels into the surface of the sheets. The polishing pad comprises a polymeric matrix made of polyurethane and hollow elastic polymeric micropheres are distributed therein. The cell size and distribution in the polishing pad made of thermoplastic foam resin highly depend on the distribution of each component in a mixture for molding and also depend on the distribution of temperature of the circular mold. It is difficult to even out the distribution of each component in a mixture for molding in a circular mold. Furthermore, because of viscoelastic property of polyurethane, a knife used in a skiving step cannot be located on the edge of the sheet precisely and subsequently influences the flatness, size and distribution of the cells. These factors reduce the batch uniformity when producing the polishing pad, and thus a polishing process involved becomes complicated. In another aspect, the cells of the polishing pad in this patent are discontinuous for each other, so that polishing fluid cannot flow smoothly and polishing particles cannot diffuse evenly. Besides, the residues formed during polishing easily stay on the surface of the polishing pad and their removal is poor; as a result, the residues scrap and damage the substrate to be polished.
U.S. Patent Application Publication No. 2004/0224623 A1 discloses a polishing pad having a plate-like shape. The polishing pad comprises fibers and a resin fixing the fibers to form the plate-like shape. The polishing pad has at least one surface layer that is substantially non-porous and comprises organic fibers and a resin fixing the organic fibers. A surface of the surface layer of the polishing pad is mechanically polished, so that the surface layer has a surface on which the organic fibers are exposed. This application also discloses layering a resin-impregnated sheet-form fiber base material and a resin-unimpregnated sheet-form fiber base material and unifying them by thermocompression molding to form a polishing pad. However, the thermocompression molding step easily leads to uneven space formed between the layers. As a result, hardness, flatness, compression ratio, elasticity, and recovery ratio of the surface of the polishing pad are all affected. The density variation of the layers thermocompression molded occurs during molding. Besides, the method of producing with the condition at high temperature (such as 300° C.) and high pressure (such as 196 kN/m) chars and hardens the surface of the polishing pad, and then the polishing pad scraps and damages the substrate to be polished. Furthermore, when producing the polishing pad, migration easily occurs and the polymers cannot be distributed in the sheet-form fiber base evenly. Heat for laminating also affects the quality, such as hardness, elasticity, compression rate, and density of the polishing pad. The factors all reduce the efficiency of polishing.
The fibers in the conventional polishing pad comprise a single polymer. For example, polyethylene terephthalate, which is a hydrophobic polymer, is usually taken for constituting the fibers. The fibers made of polyethylene terephthalate maintain the hydrophobic properties and avoid the influence of slurry when polishing. However, such fibers are hard and easy to scratch the surface of the substrate to be polished. On the contrary, nylon fibers are also common found in the polishing pad. Because nylon fibers are very soft, scratch of the surface of the substrate to be polished is avoided. However, nylon is a hydrophilic polymer, and is easy to react with the slurry and eliminates the efficiency of polishing.